The invention relates in general to sensing algorithms in automotive fuel blends.
Ethanol is a common replacement for gasoline in automotive fuel blends. However, fuel containing ethanol tends to absorb moisture from the atmosphere. Too much water condensed in the fuel causes phase separation of the gasoline and ethanol with the ethanol and water phase settled at the bottom of the fuel tank of an engine while the gasoline is at the top. If some of the ethanol and water phase is pumped through the fuel system to the engine, the engine may not ignite. Further, water corrodes engine components in time. Thus, water is a contaminant in fuel.
Current fuel sensors are important in the adjustment of the air-to-fuel (A/F) ratio. Adjustment of the A/F ratio is necessary in a vehicle whenever its fuel composition changes, such as a change in the ethanol content of the fuel. This makes the presence of a real-time on-board fuel sensor to measure the ethanol content in the fuel desirable. While current fuel sensors can be used to estimate the ethanol content, none have the capability of monitoring the water contamination in fuel that can result in phase separation.
Accordingly, a sensing algorithm, which can be added to current sensors, can monitor the water content in fuel. In doing so, it can signal the driver to prevent phase separation, i.e., the separation of gasoline from ethanol mixed with the water contaminant. Specifically, the present invention is a method for determining a level of water contamination in a fuel containing ethanol, comprising the steps of determining an ethanol concentration of the fuel; sensing a resistance of the fuel; determining a resistance limit of the fuel using the ethanol concentration; and comparing the resistance to the resistance limit to provide the level of water contamination.
In a preferred aspect, the method also comprises the step of measuring a capacitance of the fuel, and the step of determining the ethanol concentration includes the step of comparing the capacitance to values on a look-up table, the look-up table including a plurality of capacitance values and ethanol concentrations corresponding to the plurality of capacitance values.
In one aspect of the invention, the step of determining a resistance limit of the fuel using the ethanol concentration comprises the steps of comparing the ethanol concentration to values on a look-up table, the look-up table including a plurality of ethanol concentrations and resistance values corresponding to the plurality of ethanol concentrations, wherein each resistance value represents a known resistance of fuel at a known level of water contamination; and multiplying a known resistance corresponding to the ethanol concentration by an alarm fraction to obtain the resistance limit. In one variation of this aspect, the known level of water contamination is a level of water contamination just prior to a phase separation. In another variation of this aspect, the known level of water contamination is 0%.
Any of the foregoing aspects can include the step of reporting when the resistance is at or below the resistance limit. Preferably, this step comprises the step of producing an alarm.
In the aspect of the invention wherein the known resistance level corresponding to the ethanol concentration is at a level of water contamination of 0%, a further aspect includes that the alarm fraction is equal to 1.0 and the step of comparing the resistance to the resistance limit to provide the level of water contamination comprises the steps of calculating a normalized resistance by dividing the resistance by the resistance limit; and calculating a water contamination parameter, wherein the water contamination parameter=xe2x88x921.6667*(normalized resistance)+1.6667. The inventive method according to this aspect can also include the step of reporting when the water contamination parameter is greater than an alarm value, wherein 0 less than alarm value less than 1.0.
In yet another aspect of the invention, the step of calculating a resistance limit of the fuel using the ethanol concentration comprises the step of comparing the ethanol concentration to values on a look-up table, the look-up table including a plurality of ethanol concentrations and resistance values corresponding to the plurality of ethanol concentrations, wherein each resistance value represents a known resistance of fuel with no water contamination; and wherein a known resistance corresponding to the ethanol concentration is the resistance limit. In this aspect, the step of comparing the resistance to the resistance limit to provide the level of water contamination can include the steps of calculating a normalized resistance by dividing the resistance by the resistance limit; and calculating a water contamination parameter, wherein the water contamination parameter=xe2x88x921.6667*(normalized resistance)+1.6667. Preferably, this aspect also includes the step of reporting when the water contamination parameter is greater than an alarm value, wherein 0 less than alarm valuexe2x89xa61.0.
The step of reporting when the water contamination parameter is greater than an alarm value can comprise the step of producing an alarm.